i have a question about the line sizing of a chiller system i am working on currently. It involves 2 V-Coil style condenser units, so basically 4 individual condenser slabs in V formations. They are to be tied together in parallel. Usually we tie them with a single copper manifold tube that runs from the first inlet to the last, with the discharge pipe going in the middle of the manifold. My question is in regards to the size of the header manifold. From past history, it was always spec'd a size larger than the discharge line. Is this a rule of thumb when it comes down to parallel headers?! I am asking because it does not really make sense to me since now you have decreased the velocity of the oil and refrigerant. Can anyone familiar with parallel air cooled condensers give me some advice on piping them together?

Thanks!
Here is a rendering of the layout:
http://i68.tinypic.com/m8h1si.jpg

14937

polito73

22-10-2017, 06:10 AM

Hi Everybody!!
This is my first time at the forum.
I think this is intended to have an even pressure at each of the condenser inlets. Thats wy the large size of the manifold header.

Saludos

Glenn Moore

22-10-2017, 08:53 PM

When paralleling up condensers it is important to have as even as possible the pressure drop through each condenser coil. So you either fit a header as the drawing or fit 3 small headers i.e. A header to each pair of condenser coils and a main header connecting the 2 pairs of coils together keeping the pipework equal distance .
The drop in velocity is of little consequence as oil will still flow down the coils with the hot gas although your picture shows the main discharge pipe entering the header in the bottom which must be in the top to prevent liquid and oil migrating back to the compressor.
More importantly is the outlets from the 4 condenser coils as the pd's (pressure drops ) through the individual coils will be different and unless the outlet pipe work is connected correctly you will have liquid backing up in some coils and hot gas exiting the other coils causing poor system performance due to poor quality liquid at the expansion valves.
Various other factors come into play when you have multiple Condensers in parallel ie the condenser fan control must be equalised between the v coils , the air flow through the coils is impossible to predict as the weather changes and wind direction changes making certain coils more dominant due the higher wind force etc.
A simple method of balancing the coils is to fit outlet drop pipes to create liquid columns in the 4 outlets ( see Ashrea book ) the drop leg columns are normally about 3 feet from the coil outlet to the liquid line header , or if the coils are to low then where you connect the pair of coils together with a tee piece simply cut with a hacksaw through the back of the tee piece and insert a piece of copper plate the shape of a keyhole to suit the size of tee piece. The plate is then inserted into the back of the tee piece and brazed in place. This plate acts as an inducer tee, as the coil that is flowing liquid or gas from the coil will hit the plate in the tee piece and be directed down into the outlet tube, this then causes the coil which is backing up liquid to release this liquid due to the induced flow from its sister coil. This method has proved to work extremely well and virtually equalises the pd's in the coils .
I attended several plants which would not perform and it was the condensers causing the problem, in all cases it was parallel connected condensers.
Often you can measure the difference in liquid exiting the condenser coils by simply holding the two outlets before they enter the tee piece and onto the liquid line. If the temperature difference from the two condensers can be measured by your hand then you have a problem.
I have a PowerPoint presentation I wrote for training purposes I could send to you if you PM me

al

22-10-2017, 11:11 PM

Excellent post Glenn, i cant rep you unfortunately. Could i be cheeky and ask for a copy of that presentation please:o